Descriptions

Dust deposition on ecosystems with highly weathered soils may provide vital rock-derived nutrients that maintain ecosystem productivity. Because of the difficulties in measuring temporally and spatially heterogeneous dust deposition over ecologically meaningful timescales, evaluations of the spatial variability in dust deposition are extremely rare. In the Luquillo Mountains of Puerto Rico, dust originates from the Sahara-Sahel region of Africa, travelling on trade winds from the east across the Atlantic Ocean. This thesis evaluates the spatial variability of dust deposition in two ways: 1) using two twenty-year weekly records of rainfall chemistry in conjunction with historical airmass trajectory provenance, and 2) Isotopic ratios of neodymium in soil that represent mixing between neodymium from bedrock sources and from African dust. Results from rainfall chemistry show deposition can vary from 0.7 to 2.6 g dust m⁻² yr⁻¹ along a 10 km east to west transect in the Luquillo Mountains. Across 31 ridgetop locations, soil neodymium isotope ratios reveal a spatial variability in dust deposition of 1.7 to 43.2 g m⁻² yr⁻¹ in an approximately 10 x 10 km area. An analysis of several key environmental variables has not revealed a key factor that determines long-term differences in dust deposition. The most probable control on dust deposition is a complex interaction of variables such as surface wind patterns and long-term canopy characteristics.